Process depending on plasma discharges sustained by inductive coupling

ABSTRACT

A process for fabricating a product 28, 119. The process comprises the steps of subjecting a substrate to a composition of entities, at least one of the entities emanating from a species generated by a gaseous discharge excited by a high frequency field in which the vector sum of phase and anti-phase capacitive coupled voltages from the inductive coupling structure substantially balances.

CROSS REFERENCES TO RELATED APPLICATIONS

This application is a continuation-in-part of application Ser. No.08/736,315 filed Oct. 23, 1996, now abandoned, which is a continuationof application Ser. No. 08/567,224 filed Dec. 4, 1995, now abandoned.All of these documents are hereby incorporated by reference for allpurposes.

BACKGROUND OF THE INVENTION

This invention relates generally to plasma processing. Moreparticularly, the invention is for plasma processing of devices using aninductive discharge. This invention is illustrated in an example withregard to plasma etching and resist stripping of semiconductor devices.The invention also is illustrated with regard to chemical vapordeposition (CVD) of semiconductor devices. But it will be recognizedthat the invention has a wider range of applicability. Merely by way ofexample, the invention also can be applied in other plasma etchingapplications, and deposition of materials such as silicon, silicondioxide, silicon nitride, polysilicon, among others.

Plasma processing techniques can occur in a variety of semiconductormanufacturing processes. Examples of plasma processing techniques occurin chemical dry etching (CDE), ion-assisted etching (IAE), and plasmaenhanced chemical vapor deposition (PECVD), including remote plasmadeposition (RPCVD) and ion-assisted plasma enhanced chemical vapordeposition (IAPECVD). These plasma processing techniques often rely uponradio frequency power (rf) supplied to an inductive coil for providingpower to gas phase species in forming a plasma.

Plasmas can be used to form neutral species (i.e., uncharged) forpurposes of removing or forming films in the manufacture of integratedcircuit devices. For instance, chemical dry etching generally depends ongas-surface reactions involving these neutral species withoutsubstantial ion bombardment.

In other manufacturing processes, ion bombardment to substrate surfacesis often undesirable. This ion bombardment, however, is known to haveharmful effects on properties of material layers in devices andexcessive ion bombardment flux and energy can lead to intermixing ofmaterials in adjacent device layers, breaking down oxide and "wear out,"injecting of contaminative material formed in the processing environmentinto substrate material layers, harmful changes in substrate morphology(e.g. amophotization), etc.

Ion assisted etching processes, however, rely upon ion bombardment tothe substrate surface in defining selected films. But these ion assistedetching processes commonly have a lower selectivity relative toconventional CDE processes. Hence, CDE is often chosen when highselectivity is desired and ion bombardment to substrates are to beavoided.

One commonly used chemical dry etching technique is conventionalphotoresist stripping, often termed ashing or stripping. Conventionalresist stripping relies upon a reaction between a neutral gas phasespecies and a surface material layer, typically for removal. Thisreaction generally forms volatile products with the surface materiallayer for its removal. The neutral gas phase species is formed by aplasma discharge. This plasma discharge can be sustained by a coil(e.g., helical coil, etc.) operating at a selected frequency in aconventional photoresist stripper. An example of the conventionalphotoresist stripper is a quarter-wave helical resonator stripper, whichis described by U.S. Pat. No. 4,368,092 in the name of Steinberg et al.

Referring to the above, an objective in chemical dry etching is toreduce or even eliminate ion bombardment (or ion flux) to surfaces beingprocessed to maintain the desired etching selectivity. In practice,however, it is often difficult to achieve using conventional techniques.These conventional techniques generally attempt to control ion flux bysuppressing the amount of charged species in the plasma source reachingthe process chamber. A variety of techniques for suppressing thesecharged species have been proposed.

These techniques often rely upon shields, baffles, large separationdistances between the plasma source and the chamber, or the like, placedbetween the plasma source and the process chamber. The conventionaltechniques generally attempt to directly suppress charge densitydownstream of the plasma source by interfering with convective anddiffusive transport of charged species. They tend to promoterecombination of charged species by either increasing the surface area(e.g., baffles, etc.) relative to volume, or increasing flow time, whichrelates to increasing the distance between the plasma source and theprocess chamber.

These baffles, however, cause loss of desirable neutral etchant speciesas well. The baffles, shields, and alike, also are often cumbersome.Baffles, shields, or the large separation distances also causeundesirable recombinative loss of active species and sometimes causeradio frequency power loss and other problems. These baffles and shieldsalso are a potential source of particulate contamination, which is oftendamaging to integrated circuits.

Baffles, shields, spatial separation, and alike, when used alone alsoare often insufficient to substantially prevent unwanted parasiticplasma currents. These plasma currents are generated between the waferand the plasma source, or between the plasma source and walls of thechamber. It is commonly known that when initial charged species levelsare present in an electrical field, the charged species are acceleratedand dissociative collisions with neutral particles can multiply theconcentration of charge to higher levels. If sufficient "seed" levels ofcharge and rf potentials are present, the parasitic plasma in thevicinity of the process wafer can reach harmful charge density levels.In some cases, these charge densities may be similar to or even greaterthan plasma density within the source plasma region, thereby causingeven more ion flux to the substrate.

Charge densities also create a voltage difference between the plasmasource and processing chamber or substrate support, which can have anadditional deleterious effect. This voltage difference enhances electricfields that can accelerate extraction of charge from the plasma source.Hence, their presence often induces increased levels of charge to beirregularly transported from the plasma source to process substrates,thereby causing non-uniform ion assisted etching.

Conventional ion assisted plasma etching, however, often requirescontrol and maintenance of ion flux intensity and uniformity withinselected process limits and within selected process energy ranges.Control and maintenance of ion flux intensity and uniformity are oftendifficult to achieve using conventional techniques. For instance,capacitive coupling between high voltage selections of the coil and theplasma discharge often cause high and uncontrollable plasma potentialsrelative to ground. It is generally understood that voltage differencebetween the plasma and ground can cause damaging high energy ionbombardment of articles being processed by the plasma, as illustrated byU.S. Pat. No. 5,234,529 in the name of Johnson. It is further oftenunderstood that rf component of the plasma potential varies in timesince it is derived from a coupling to time varying rf excitation.Hence, the energy of charged particles from plasma in conventionalinductive sources is spread over a relatively wide range of energies,which undesirably tends to introduce uncontrolled variations in theprocessing of articles by the plasma.

The voltage difference between the region just outside of a plasmasource and the processing chamber can be modified by introducinginternal conductive shields or electrode elements into the processingapparatus downstream of the source. When the plasma potential iselevated with respect to these shield electrodes, however, there is atendency to generate an undesirable capacitive discharge between theshield and plasma source. These electrode elements are often a source ofcontamination and the likelihood for contamination is even greater whenthere is capacitive discharge (ion bombardment from capacitive dischargeis a potential source of sputtered material). Contamination is damagingto the manufacture of integrated circuit devices.

Another limitation is that the shield or electrode elements generallyrequire small holes therein as structural elements. These small holesare designed to allow gas to flow therethrough. The small holes,however, tend to introduce unwanted pressure drops and neutral speciesrecombination. If the holes are made larger, the plasma from the sourcetends to survive transport through the holes and unwanted downstreamcharge flux will often result. In addition, undesirable discharges tothese holes in shields can, at times, produce an even more undesirablehollow cathode effect.

In conventional helical resonator designs, conductive external shieldsare interposed between the inductive power (e.g., coil, etc.) and wallsof the vacuum vessel containing the plasma. A variety limitations withthese external capacitive shielded plasma designs (e.g., helicalresonator, inductive discharge, etc.) have been observed. In particular,the capacitively shielded design often produces plasmas that aredifficult to tune and even ignite. Alternatively, the use of unshieldedplasma sources (e.g., conventional quarter-wave resonator, conventionalhalf-wave resonator, etc.) attain a substantial plasma potential fromcapacitive coupling to the coil, and hence are prone to createuncontrolled parasitic plasma currents to grounded surfaces.Accordingly, the use of either the shielded or the unshielded sourcesusing conventional quarter and half-wave rf frequencies produceundesirable results.

In many conventional plasma sources a means of cooling is required tomaintain the plasma source and substrates being treated below a maximumtemperature limit. Power dissipation in the structure causes heating andthereby increases the difficulty and expense of implementing effectivecooling means. Inductive currents may also be coupled from theexcitation coil into internal or capacitive shields and these currentsare an additional source of undesirable power loss and heating.Conventional capacitive shielding in helical resonator dischargesutilized a shield which was substantially split along the long axis ofthe resonator to lessen eddy current loss. However, such a shieldsubstantially perturbs the resonator characteristics owing to unwantedcapacitive coupling and current which flows from the coil to the shield.Since there are no general design equations, nor are propertiescurrently known for resonators which are "loaded" with a shield alongthe axis, sources using this design must be sized and made to work bytrial and error.

In inductive discharges, it is highly desirable to be able tosubstantially control the plasma potential relative to ground potential,independent of input power, pressure, gas composition and othervariables. In many cases, it is desired to have the plasma potential besubstantially at ground potential (at least offset from ground potentialby an amount insignificantly different from the floating potential orintrinsic DC plasma potential). For example, when a plasma source isutilized to generate neutral species to be transported downstream of thesource for use in ashing resist on a semiconductor device substrate (awafer or flat panel electronic display), the concentration and potentialof charged plasma species in the reaction zone are desirably reduced toavoid charging damage from electron or ionic current from the plasma tothe device. When there is a substantial potential difference betweenplasma in the source and grounded surfaces beyond the source, there is atendency for unwanted parasitic plasma discharges to form outside of thesource region.

Another undesirable effect of potential difference is the accelerationof ions toward grounded surfaces and subsequent impact of the energeticions with surfaces. High energy ion bombardment may cause lattice damageto the device substrate being processed and may cause the chamber wallor other chamber materials to sputter and contaminate device wafers. Inother plasma processing procedures, however, some ion bombardment may benecessary or desirable, as is the case particularly for anisotropicion-induced plasma etching procedures (for a discussion of ion-enhancedplasma etching mechanisms See Flamm (Ch. 2, pp.94-183 in Plasma Etching,An Introduction, D. M. Manos and D. L. Flamm, eds., Academic Press,1989)). Consequently, uncontrolled potential differences, such as thatcaused by "stray" capacitive coupling from the coil of an inductiveplasma source to the plasma, are undesirable.

Referring to the above limitations, conventional plasma sources alsohave disadvantages when used in conventional plasma enhanced CVDtechniques. These techniques commonly form a reaction of a gascomposition in a plasma discharge. One conventional plasma enhancedtechnique relies upon ions aiding in rearranging and stabilizing thefilm, provided the bombardment from the plasma is not sufficientlyenergetic to damage the underlying substrate or the growing film.Conventional resonators and other types of inductive discharges oftenproduce parasitic plasma currents from capacitive coupling, which oftendetrimentally influences film quality, e.g., an inferior film, etc.These parasitic plasma currents are often uncontrollable, and highlyundesirable. These plasma sources also have disadvantages in otherplasma processing techniques such as ion-assisted etching, and others.Of course, the particular disadvantage will often depend upon theapplication.

To clarify certain concepts used in this application, it will beconvenient to introduce these definitions.

Ground (or ground potential): These terms are defined as a referencepotential which is generally taken as the potential of a highlyconductive shield or other highly conductive surface which surrounds theplasma source. To be a true ground shield in the sense of thisdefinition, the RF conductance at the operating frequency is oftensubstantially high so that potential differences generated by currentwithin the shield are of negligible magnitude compared to potentialsintentionally applied to the various structures and elements of theplasma source or substrate support assembly. However, some realizationsof plasma sources do not incorporate a shield or surface with adequateelectrical susceptance to meet this definition. In implementations wherethere is a surrounding conductive surface that is somewhat similar to aground shield or ground plane, the ground potential is taken to be thefictitious potential which the imperfect grounded surface would haveequilibrated to if it had zero high frequency impedance. In designswhere there is no physical surface which is adequately configured orwhich does not have insufficient susceptance to act as a "ground"according to the above definition, ground potential is the potential ofa fictitious surface which is equi-potential with the shield or "ground"conductor of an unbalanced transmission line connection to the plasmasource at its RF feed point. In designs where the plasma source isconnected to an RF generator with a balanced transmission line RF feed,"ground" potential is the average of the driven feed line potentials atthe point where the feed lines are coupled to the plasma source.

Inductively Coupled Power: This term is defined as power transferred tothe plasma substantially by means of a time-varying magnetic flux whichis induced within the volume containing the plasma source. Atime-varying magnetic flux induces an electromotive force in accord withMaxwell's equations. This electromotive force induces motion byelectrons and other charged particles in the plasma and thereby impartsenergy to these particles.

RF inductive power source and bias power supply: In most conventionalinductive plasma source reactors, power is supplied to an inductivecoupling element (the inductive coupling element is often a multi-turncoil which abuts a dielectric wall containing a gas where the plasma isignited at low pressure) by an rf power generator.

Conventional Helical Resonator: Conventional helical resonator can bedefined as plasma applicators. These plasma applicators have beendesigned and operated in multiple configurations, which were describedin, for example, U.S. Pat. No. 4,918,031 in the names of Flamm et al.,U.S. Pat. No. 4,368,092 in the name of Steinberg et al., U.S. Pat. No.5,304,282 in the name of Flamm, U.S. Pat. No. 5,234,529 in the name ofJohnson, U.S. Pat. No. 5,431,968 in the name of Miller, and others. Inthese configurations, one end of the helical resonator applicator coilhas been grounded to its outer shield. In one conventionalconfiguration, a quarter wavelength helical resonator section isemployed with one end of the applicator coil grounded and the other endfloating (i.e., open circuited). A trimming capacitance is sometimesconnected between the grounded outer shield and the coil to "fine tune"the quarter wave structure to a desired resonant frequency that is belowthe native resonant frequency without added capacitance. In anotherconventional configuration, a half-wavelength helical resonator sectionwas employed in which both ends of the coil were grounded. The functionof grounding the one or both ends of the coil was believed to be notessential, but advantageous to "stabilize the plasma operatingcharacteristics" and "reduce the possibility of coupling stray currentto nearby objects." See U.S. Pat. No. 4,918,031.

Conventional resonators have also been constructed in other geometricalconfigurations. For instance, the design of helical resonators with ashield of square cross section is described in Zverev et al., IRETransactions on Component Parts, pp. 99-110, Sept. 1961. Johnson (U.S.Pat. No. 5,234,529) teaches that one end of the cylindrical spiral coilin a conventional helical resonator may be deformed into a planar spiralabove the top surface of the plasma reactor tube. U.S. Pat. No.5,241,245 in the names of Barnes et al. teach the use of conventionalhelical resonators in which the spiral cylindrical coil is entirelydeformed into a planar spiral arrangement with no helical coil componentalong the sidewalls of the plasma source (this geometry has often beenreferred to as a "transformer coupled plasma," termed a TCP).

From the above it is seen that an improved technique, including a methodand apparatus, for plasma processing is often desired.

SUMMARY OF THE INVENTION

The present invention provides a technique, including a method andapparatus, for fabricating a product using a plasma discharge. Thepresent technique relies upon the control of the instantaneous plasma ACpotential to selectively control a variety of plasma characteristics.These characteristics include the amount of neutral species, the amountof charged species, overall plasma potential, the spatial extent anddistribution of plasma density, the distribution of electrical current,and others. This technique can be used in applications includingchemical dry etching (e.g., stripping, etc.), ion-enhanced etching,plasma immersion ion implantation, chemical vapor deposition andmaterial growth, and others.

In one aspect of the invention, a process for fabricating a product isprovided. These products include a varieties of devices (e.g.,semiconductor, flat panel displays, micro-machined structures, etc.) andmaterials, e.g., diamonds, raw materials, plastics, etc. The processincludes steps of subjecting a substrate to a composition of entities.At least one of the entities emanates from a species generated by agaseous discharge excited by a high frequency field in which the vectorsum of phase and anti-phase capacitive coupled voltages (e.g., AC plasmavoltage) from the inductive coupling structure substantially balances.This process provides for a technique that is substantially free fromstray or parasitic capacitive coupling from the plasma source to chamberbodies (e.g., substrate, walls, etc.) at or near ground potential.

In another aspect of the invention, another process for fabricating aproduct is provided. The process includes steps of subjecting asubstrate to a composition of entities. At least one of the entitiesemanates from a species generated by a gaseous discharge excited by ahigh frequency field in which the vector sum of phase and anti-phasecapacitive coupled voltages from the inductive coupling structure isselectively maintained. This process provides for a technique that canselectively control the amount of capacitive coupling to chamber bodiesat or near ground potential.

A further aspect of the invention provides yet another process forfabricating a product. This process includes steps of subjecting asubstrate to a composition of entities. At least one of the entitiesemanates from a species generated by a gaseous discharge excited by ahigh frequency field in which the vector sum of phase and anti-phasecapacitive coupled voltages from the inductive coupling structure isselectively maintained. A further step of selectively applying a voltagebetween the at least one of the entities in the plasma source and asubstrate is provided. This process provides for a technique that canselectively control the amount of capacitive coupling to chamber bodiesat or near ground potential, and provide for a driving voltage betweenthe entities and a substrate.

Another aspect of the invention provides another process for fabricatinga product. The process comprises steps of subjecting a substrate to acomposition of entities and using the resulting substrate for completionof the product. At least one of the entities emanates from a speciesgenerated by a gaseous discharge provided by a plasma applicator, e.g.,a helical resonator, inductive coil, transmission line, etc. This plasmaapplicator has an integral current driven by capacitive coupling of aplasma column to elements with a selected potential greater than asurrounding shield potential substantially equal to capacitive couplingof the plasma column to substantially equal elements with a potentialbelow shield potential.

In a further aspect, the invention provides an apparatus for fabricatinga product. The apparatus has an enclosure comprising an outer surfaceand an inner surface. The enclosure houses a gaseous discharge. Theapparatus also includes a plasma applicator (e.g., helical coil,inductive coil, transmission line, etc.) disposed adjacent to the outersurface. A high frequency power source operably coupled to the plasmaapplicator is included. The high frequency power source provides highfrequency to excite the gaseous discharge to provide at least one entityfrom a high frequency field in which the vector sum of phase andanti-phase capacitive current coupled from the inductive couplingstructure is selectively maintained.

In another aspect, the present invention provides an improved plasmadischarge apparatus. This plasma discharge apparatus includes a plasmasource, a plasma applicator (e.g., inductive coil, transmission line,etc.), and other elements. This plasma applicator provides a de-coupledplasma source. A wave adjustment circuit (e.g., RLC circuit, coil,transmission line, etc.) is operably coupled to the plasma applicator.The wave adjustment circuit can selectively adjust phase and anti-phasepotentials of the plasma from an rf power supply. This rf power supplyis operably coupled to the wave adjustment circuit.

The present invention achieves these benefits in the context of knownprocess technology. However, a further understanding of the nature andadvantages of the present invention may be realized by reference to thelatter portions of the specification and attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified diagram of a plasma etching apparatus accordingto the present invention;

FIGS. 2A-2E are simplified configurations using wave adjustment circuitsaccording to the present invention;

FIG. 3 is a simplified diagram of a chemical vapor deposition apparatusaccording to the present invention;

FIG. 4 is a simplified diagram of a stripper according to the presentinvention;

FIGS. 5A-5C are more detailed simplified diagrams of a helical resonatoraccording to the present invention;

FIG. 6 is a conventional quarter-wave helical resonator plasma etchingapparatus with stray plasma which results from the coupling in theconventional design;

FIG. 7 is a simplified diagram of the rf voltage distribution along thecoil of the FIG. 6 apparatus;

FIG. 8 is a simplified top-view diagram of a stripping apparatusaccording to the present experiments; and

FIG. 9 is a simplified side-view diagram of a stripping apparatusaccording to the present experiments.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is a simplified diagram of a plasma etch apparatus 10 accordingto the present invention. This etch apparatus is provided with aninductive applicator, e.g., inductive coil. This etch apparatusdepicted, however, is merely an illustration, and should not limit thescope of the claims as defined herein. One of ordinary skilled in theart may implement the present invention with other treatment chambersand the like.

The etch apparatus includes a chamber 12, a feed source 14, an exhaust16, a pedestal 18, an inductive applicator 20, a radio frequency (rf)power source 22 to the inductive applicator 20, wave adjustment circuits24, 29 (WACs), a radio frequency power source 35 to the pedestal 18, acontroller 36, and other elements. Optionally, the etch apparatusincludes a gas distributor 17.

The chamber 12 can be any suitable chamber capable of housing a product28, such as a wafer to be etched, and for providing a plasma dischargetherein. The chamber can be a domed chamber for providing a uniformplasma distribution over the product 28 to be etched, but the chamberalso can be configured in other shapes or geometries, e.g., flatceiling, truncated pyramid, cylindrical, rectangular, etc. Dependingupon the application, the chamber is selected to produce a uniformentity density over the pedestal 18, providing a high density ofentities (i.e., etchant species) for etching uniformity.

The present chamber includes a dome 25 having an interior surface 26made of quartz or other suitable materials. The exterior surface of thechamber is typically a dielectric material such as a ceramic or thelike. Chamber 12 also includes a process kit with a focus ring 32, acover (not shown), and other elements. Preferably, the plasma dischargeis derived from the inductively coupled plasma source that is ade-coupled plasma source (DPS) or a helical resonator, although othersources can be employed.

The de-coupled source originates from rf power derived from theinductive applicator 20. Inductively coupled power is derived from thepower source 22. The rf signal frequencies ranging from 800 kHz to 80MHz can be provided to the inductive applicator 20. Preferably, the rfsignal frequencies range from 5 MHz to 60 MHz. The inductive applicator(e.g., coil, antenna, transmission line, etc.) overlying the chamberceiling can be made using a variety of shapes and ranges of shapes. Forexample, the inductive applicator can be a single integral conductivefilm, a transmission line, or multiple coil windings. The shape of theinductive applicator and its location relative to the chamber areselected to provide a plasma overlying the pedestal to improve etchuniformity.

The plasma discharge (or plasma source) is derived from the inductiveapplicator 20 operating at selected phase 23 and anti-phase 27potentials (i.e., voltages) that substantially cancel each other. Thecontroller 36 is operably coupled to the wave adjustment circuits 24,29. In one embodiment, wave adjustment circuits 24, 29 provide aninductive applicator operating at full-wave multiples 21. Thisembodiment of full-wave multiple operation provides for balancedcapacitance of phase 23 and anti-phase voltages 27 along the inductiveapplicator (or coil adjacent to the plasma). This full-wave multipleoperation reduces or substantially eliminates the amount of capacitivelycoupled power from the plasma source to chamber bodies (e.g., pedestal,walls, wafer, etc.) at or close to ground potential. Alternatively, thewave adjustment circuits 24, 29 provide an inductive applicator that iseffectively made shorter or longer than a full-wave length multiple by aselected amount, thereby operating at selected phase and anti-phasevoltages that are not full-wave multiples. Alternatively, more than two,one or even no wave adjustment circuits can be provided in otherembodiments. But in all of these above embodiments, the phase andanti-phase potentials substantially cancel each other, thereby providingsubstantially no capacitively coupled power from the plasma source tothe chamber bodies.

In alternative embodiments, the wave adjustment circuit can beconfigured to provide selected phase and anti-phase coupled voltagescoupled from the inductive applicator to the plasma that do not cancel.This provides a controlled potential between the plasma and the chamberbodies, e.g., the substrate, grounded surfaces, walls, etc. In oneembodiment, the wave adjustment circuits can be used to selectivelyreduce current (i.e., capacitively coupled current) to the plasma. Thiscan occur when certain high potential difference regions of theinductive applicator to the plasma are positioned (or kept) away fromthe plasma region (or inductor-containing-the-plasma region) by makingthem go into the wafer adjustment circuit assemblies, which aretypically configured outside of the plasma region. In this embodiment,capacitive current is reduced and a selected degree of symmetry betweenthe phase and anti-phase of the coupled voltages is maintained, therebyproviding a selected potential or even substantially ground potential.In other embodiments, the wave adjustment circuits can be used toselectively increase current (i.e., capacitively coupled current) to theplasma.

As shown, the wave adjustment circuits are attached (e.g., connected,coupled, etc.) to ends of the inductive applicator. Alternatively, eachof these wave adjustment circuits can be attached at an intermediateposition away from the inductive application ends. Accordingly, upperand lower tap positions for respective wave adjustment circuits can beadjustable. But both the inductive applicator portions below and aboveeach tap position are active. That is, they both can interact with theplasma discharge.

A sensing apparatus can be used to sense plasma voltage and useautomatic tuning of the wave adjustment circuits and any rf matchingcircuit between the rf generator and the plasma treatment chamber. Thissensing apparatus can maintain the average AC potential at zero or aselected value relative to ground or any other reference value. Thiswave adjustment circuit provides for a selected potential differencebetween the plasma source and chamber bodies. These chamber bodies maybe at a ground potential or a potential supplied by another bias supply,e.g., See FIG. 1 reference numeral 35. Examples of wave adjustmentcircuits are described by way of the FIGS. below.

For instance, FIGS. 2A to 2E are simplified configurations using thewave adjustment circuits according to the present invention. Thesesimplified configurations should not limit the scope of the claimsherein. In an embodiment, these wave adjustment circuits employsubstantially equal circuit elements (e.g., inductors, capacitors,transmission line sections, and others) such that the electrical lengthof the wave adjustment circuits in series with the inductive applicatorcoupling power to the plasma is substantially an integral multiple ofone wavelength. In other embodiments, the circuit elements provide forinductive applicators at other wavelength multiples, e.g.,one-sixteenth-wave, one-eighth-wave, quarter-wave, half-wave,three-quarter wave, etc. In these embodiments (e.g., full-wave multiple,half-wave, quarter-wave, etc.), the phase and anti-phase relationshipbetween the plasma potentials substantially cancel each other. Infurther embodiments, the wave adjustment circuits employ circuitelements that provide plasma applicators with phase and anti-phasepotential relationships that do not cancel each other out using avariety of wave length portions.

FIG. 2A is a simplified illustration of an embodiment 50 using waveadjustment circuits according to the present invention. This embodiment50 includes a discharge tube 52, an inductive applicator 55, an exteriorshield 54, an upper wave adjustment circuit 57, a lower wave adjustmentcircuit 59, an rf power supply 61, and other elements. The upper waveadjustment circuit 57 is a helical coil transmission line portion 69,outside of the plasma source region 60. Lower wave adjustment circuit 59also is a helical coil transmission line portion 67 outside of theplasma source region 60. The power supply 61 is attached 65 to thislower helical coil portion 67, and is grounded 63. Each of the waveadjustment circuits also are shielded 66, 68.

In this embodiment, the wave adjustment circuits are adjusted to providesubstantially zero AC voltage at one point on the inductive coil (referto point 00 in FIG. 2A). This embodiment also provides substantiallyequal phase 70 and anti-phase 71 voltage distributions in directionsabout this point (refer to 00-A and 00-C in FIG. 2A) and providessubstantially equal capacitance coupling to the plasma from physicalinductor elements (00-C) and (00-A), carrying the phase and anti-phasepotentials. Voltage distributions 00-A and 00-C are combined with C-Dand A-B (shown by the phantom lines) would substantially comprise afull-wave voltage distribution in this embodiment where the desiredconfiguration is a selected phase/antiphase portion of a full-waveinductor (or helical resonator) surrounding the plasma source dischargetube.

In this embodiment, it is desirable to reduce or minimize capacitivecoupling current from the inductive element to the plasma discharge inthe plasma source. Since the capacitive current increases monotonicallywith the magnitude of the difference of peak phase and anti-phasevoltages, which occur at points A and C in FIG. 2A, this coupling can belessened by reducing this voltage difference. In FIG. 2A, for example,it is achieved by way of two wave adjustment circuits 57, 59. Coil 55(or discharge source) is a helical resonator and the wave adjustmentcircuits 57, 59 are helical resonators.

The discharge source helical resonator 53 can be constructed usingconventional design formulae. Generally, this helical resonator includesan electrical length which is a selected phase portion "x" (A to 00 toC) of a full-wave helical resonator. The helical resonator waveadjustment circuits are each selected to comprise a portion (2-x) offull-wave helical resonators. Physical parameters for the waveadjustment helical resonators can be selected to realize practicalphysical dimensions and appropriate Q, Z_(o), etc values. In particular,some or even all of the transmission line parameters (Q, Z_(o), etc.) ofthe wave adjustment circuit sections may be selected to be substantiallythe same as the transmission line parameters of the inductiveapplicator. The portion of the inductive plasma applicator helicalresonator, on the other hand, is designed and sized to provide selecteduniformity values over substrate dimensions within an economicalequipment size and reduced Q.

The wave adjustment circuit provides for external rf power coupling,which can be used to control and match power to the plasma source, ascompared to conventional techniques used in helical resonators and thelike. In particular, conventional techniques often match to, couplepower to, or match to the impedance of the power supply to the helicalresonator by varying a tap position along the coil above the groundedposition, or selecting a fixed tap position relative to a grounded coilend and matching to the impedance at this position using a conventionalmatching network, e.g., LC network, network, etc. Varying this tapposition along the coil within a plasma source is often cumbersome andgenerally imposes a difficult mechanical design problems. Using thefixed tap and external matching network also is cumbersome and can causeunanticipated changes in the discharge Q, and therefore influences itsoperating mode and stability. In the present embodiments, the waveadjustment circuits can be positioned outside of the plasma source (orconstrained in space containing the inductive coil, e.g., See FIG. 2A.Accordingly, the mechanical design (e.g., means for varying tapposition, change in the effective rf power coupling point by electricalmeans, etc.) of the tap position are simplified relative to thoseconventional techniques.

In the present embodiment, rf power is fed into the lower waveadjustment circuit 59. Alternatively, rf power can be fed into the upperwave adjustment circuit (not shown). The rf power also can be coupleddirectly into the inductive plasma coupling applicator (e.g., coil,etc.) in the wave adjustment circuit design, as illustrated by FIG. 2B.Alternatively, other application will use a single wave adjustmentcircuit, as illustrated by FIG. 2C. Power can be coupled into this waveadjustment circuit or by conventional techniques such as a tap in thecoil phase. In some embodiments, this tap in the coil phase ispositioned above the grounded end. An external impedance matchingnetwork may then be operably coupled to the power for satisfactory powertransfer efficiency from, for example, a conventional coaxial cable toimpedances (current to voltage rations) existing between the waveadjustment circuit terminated end of the applicator.

A further embodiment using multiple inductive plasma applicators also isprovided, as shown in FIG. 2D. This embodiment includes multiple plasmaapplicators (PA1, PA2 . . . PAn). These plasma applicators respectivelyprovide selected combinations of inductively coupled power andcapacitively coupled power from respective voltage potentials (V1, V2 .. . Vn). Each of these plasma applicators derives power from its powersource (PS1, PS2 . . . PSn) either directly through an appropriatematching or coupling network or by coupling to a wave adjustment circuitas described. Alternatively, a single power supply using power splittersand impedance matching networks can be coupled to each (or more thantwo) of the plasma applicators. Alternatively, more than one powersupply can be used where at least one power supply is shared among morethan one plasma applicator. Each power source is coupled to itsrespective wave adjustment circuits (WAC1, WAC2 . . . WACn).

Generally, each plasma applicator has an upper wave adjustment circuit(e.g., WAC 1a, WAC 2a . . . WACna) and a lower wave adjustment circuit(e.g., WAC1b, WAC2b . . . WACnb). The combination of upper and lowerwave adjustment circuits are used to adjust the plasma source potentialfor each plasma source zone. Alternatively, a single wave adjustmentcircuit can be used for each plasma applicator. Each wave adjustmentcircuit can provide substantially the same impedance characteristics, orsubstantially distinct impedance characteristics. Of course, theparticular configuration used will depend upon the application.

For instance, multiple plasma applicators can be used to employ distinctexcitation frequencies for selected zones in a variety of applications.These applications include film deposition using plasma enhancedchemical deposition, etching by way of ion enhanced etching or chemicaldry etching and others. Plasma cleaning also can be performed by way ofthe multiple plasma applicators. Specifically, at least one of theplasma applicators will define a cleaning plasma used for cleaningpurposes. In one embodiment, this cleaning plasma can have an oxygencontaining species. This cleaning plasma is defined by using an oxygendischarge, which is sustained by microwave power to a cavity or resonantmicrowave chamber abutting or surrounding a conventional dielectricvessel. Of course, a variety of other processes also can be performed byway of this multiple plasma applicator embodiment.

This present application using multiple plasma applicators can provide amulti-zone (or multi-chamber) plasma source without the use ofconventional mechanical separation means (e.g., baffles, separateprocess chambers, etc.). Alternatively, the degree of interactionbetween adjacent zones or chambers can be relaxed owing to the use ofvoltage potential control via wave adjustment circuits. This plasmasource provides for multiple plasma source chambers, each with its owncontrol via its own plasma applicator. Accordingly, each plasmaapplicator provides a physical zone region (i.e., plasma source) withselected plasma characteristics (e.g., capacitively coupled current,inductively coupled current, etc.). These zones can be used alone or canbe combined with other zones. Of course, the particular configurationwill depend upon the application.

In the present embodiments, the wave adjustment circuit can be made fromany suitable combination of element(s) such as various types oftransmission lines, circuits, etc. These transmission lines includeconventional solid or air dielectric coaxial cable, or ordinary,repeating inductor/capacitor discrete approximations to transmissionlines, and others. These types of transmission lines are co-axialtransmission lines, balanced parallel transmission lines, so called slowwave transmission lines with a spiral inner conductor (e.g., selectedportions of a helical resonator, etc.), and others. Individual lumped,fixed, or adjustable combinations of resistors, capacitors, andinductors (e.g., matching networks, etc.) also can be used in place oftransmission line sections for the wave adjustment circuit. Thesegeneral types of wave adjustment circuits are frequency dependent, andcan be termed frequency dependent wave adjustment circuits (or FDWACs).

Frequency independent elements also can be used as the wave adjustmentcircuits. These wave adjustment circuits can be termed frequencyindependent WACs (or FIWACs). Frequency independent wave adjustmentcircuits include degenerate cases such as short-circuit connections toground or an infinite impedance (i.e., open circuit), and others.Frequency independent wave adjustment circuits can be used alone, or incombination with the frequency dependent wave adjustment circuits.Alternatively, the frequency dependent wave adjustment circuits can beused alone or in combination with other wave adjustment circuits. Othervariations, alternative constructions, and modifications also may bepossible depending upon the application.

With regard to operation of the wave adjustment circuits, variousembodiments can be used, as illustrated by FIG. 2E. The wave adjustmentcircuits are used to select a wave length portion to be applied in theplasma applicator. In some embodiments, the average rf plasma potentialis maintained close to ground potential by providing substantially equalphase 90, 81 and anti-phase 91, 82 capacitively coupled portions of theinductive applicator. This can occur in multi-wave embodiments 92,full-wave embodiments 93, half-wave multiple embodiments, quarter-wavemultiple embodiments, or any other embodiments 94.

In alternative embodiments, it is desirable to maintain an elevatedsource plasma voltage relative to ground potential to induce acontrolled ion plasma flux (or ion bombardment) to the product substrate(or any other chamber bodies). These embodiments are provided byselecting distinct electrical lengths for each of the wave adjustmentcircuit sections such that the capacitive coupled current from a phasesection of the inductive plasma applicator is in excess of capacitivecoupled current from its anti-phase portion. In these embodiments, thewave adjustment circuit provides a deliberate imbalance between thephase and anti-phase of the coupled voltages. In some embodiments 97,this occurs by shifting the zero voltage nodes along the process chamberaxially, thereby achieving a bias relative to the plasma discharge. Asshown, the phase 95 is imbalanced relative to its anti-phase 96. Inother embodiments 99, one phase portion 84 is imbalanced by way of adifferent period relative to its complementary phase portion 85. Otherembodiments are provided where the source plasma voltage is lowerrelative to ground potential. In the embodiments were imbalance isdesirable, the potential difference between the phase and anti-phasepotential portions is reduced (or minimized) when the amount ofsputtering (e.g., wall sputtering, etc.) is reduced. The amount ofsputtering, however, can be increased (or maximized) by increasing thepotential difference between the phase and anti-phase potentialportions. Sputtering is desirable in, for example, sputtering a quartztarget, cleaning applications, and others. Of course, the type ofoperation used will depend upon the application.

Current maxima on an inductive applicator with distributed capacitance(e.g., helical resonator transmission line, etc.) occur at voltageminima. In particular, conventional quarter-wave helical resonatorcurrent is substantially at a relative maximum at its grounded end ofthe coil, and to a lesser extend in the nearby coil elements. Therefore,partial inductive coupling of power, if it occurs, will tend to be atthis grounded end. In conventional half-wave helical resonators,inductive coupling tends to occur at each of the two grounded ends.

In the present invention, substantially anti-symmetric phase andanti-phase inductive half-wave and other fractional wave applicatorsections support substantially more inductive coupling at a selected rfvoltage node, e.g., FIG. 2A reference numeral 00. This effect is causedby high current flow in the inductor applicator zones (or sections) bothdirectly above and below the node (corresponding to inductor elements inthe phase and anti-phase sections at and immediately adjacent to the rfvoltage zero point). It should be noted that conventional quarter andhalf-wave inductively coupled inductive applicators have inductivecoupling which abruptly declines below the grounded coil locationsbecause the coil terminates and voltage extrema are present at theselocations. This generally produces conventional quarter and half-wavehelical resonators that tend to operate in a capacitive mode, or with asubstantial fraction of power which is capacitively coupled to theplasma, unless the plasma is shielded from coil voltages, as notedabove.

In a specific embodiment, the power system includes selected circuitelements for effective operation. The power system includes an rf powersource. This rf power source can be any suitable rf generator capable ofproviding a selected or continuously variable frequency in a range fromabout 800 kHz to about 80 MHz. Many generators are useful. Preferably,generators capable of operating into short and open-circuit loadswithout damage are used for industrial applications. One example of asuitable generator is a fixed frequency rf generator 28.12 MHz-3 kWCX-3000 power supply made by Comdel, Inc. of Beverly, Mass. A suitablevariable frequency power supply arrangement capable of the 3 kW outputover an 800 kHz to 50 MHz range can be made by driving an IFI ModelTCCX3500 High

Power Wide Band Amplifier with a Hewlett Packard HP116A, 0-50 MHzPulse/Function Generator. Other generators including those capable ofhigher or lower power also can be used depending upon the application.

Power from the generator can be transmitted to the plasma source byconventional coaxial cable transmission line. An example of thistransmission line is RG8/U and other higher temperature rated cable(e.g., RG1151U, etc.) with a coaxial TEFLON dielectric. In someembodiments, power is fed to conventional end-grounded half-wave helicalresonators by positioning a movable tap on the helical coil andconnecting a power source between the tap and the ground. In otherembodiments, matching networks can be introduced between the coaxialcable power feed and the helical coil tap for flexibility. The matchingnetwork will depend on the selected wave configuration and waveadjustment circuits. In a balanced half-wave helical resonatorembodiment, for example, the ends of the resonator coil can beterminated with wave adjustment circuits which substantially have zerosusceptance. In particular, the wave adjustment circuit is designed asan open circuit by making no electrical connections to the ends of thecoil, or establishing an electrical equivalence thereof. Alternatively,the ends of the coil are isolated by chokes series resistance, therebyDC coupled to a fixed reference potential. These types of waveadjustment circuits are frequency independent and are "degenerate"cases. In these embodiments, the rf power is provided such that thephase and anti-phase current flows above and below the electricalmidpoint of the coil. This provides for substantially balanced phase andanti-phase current flow from the power source stabilizing desiredoperation in coil voltages above the midpoint of the coil, and alsoprovides substantially equal phase and anti-phase voltages.

The embodiments described above also can be applied to other plasmaprocessing applications, e.g., PECVD, plasma immersion ion implantation(PIII), stripping, sputtering, etc. For instance, FIG. 3 is a simplifiedCVD apparatus 100 according to the present invention. The present CVDapparatus includes a chamber 112, a feed source 114, an exhaust 116, apedestal 118, a power source 122, a ground 124, a helical resonator 126,and other elements. The helical resonator 126 has a coil 132, an outershield 133, and other elements. The chamber can be any suitable chambercapable of housing a product 119 such as a wafer for deposition, and forproviding a plasma discharge therein. Preferably, the chamber is a rightcircular cylinder chamber for providing an uniform plasma speciesdistribution over the product. But the chamber can also be configured inthe form of rectangular right cylinder, a truncated cone, and the like.The chamber and fixtures are constructed from aluminum and quartz, andother suitable materials. The plasma discharge is derived from a plasmasource which is preferably a helical resonator discharge or otherinductive discharge using a wave adjustment circuit or other techniquesto selectively adjust phase-anti-phase potentials. The present CVDapparatus provides for deposition of a dielectric material, e.g.,silicon dioxide or the like.

The product 119 having an upper surface 130 is placed into the presentCVD apparatus for deposition, e.g., plasma enhanced chemical vapordeposition (PECVD), and others. Examples of deposition materials includea dielectric material such as a silicon dioxide (SiO₂), aphosphosilicate glass (PSG), a borophosphosilicate glass (BPSG), asilicon nitride (Si₃ N₄), among others.

In one embodiment, the deposition occurs by introducing a mixturecomprising organic silane, oxygen, and an inert gas such as helium orargon according to the present invention. The organic silane can be anysuitable organic silicate material such TEOS, HMDS, OMCTS, and the like.Deposition is also conformal in selected instances. As for the oxygen,it includes a flow rate of about 1 liter/per minute and less. A relativeflow rate between the organic silane such as TEOS and oxygen ranges fromabout 1:40 to about 2:1, and is preferably less than about 1:2 incertain applications. A deposition temperature of the organicsilane-oxygen layer ranges from about 300 to about 500° C., and can alsobe at other temperatures. Pressures in the range of 1 to 7 Torr aregenerally used. Of course, other concentrations, temperatures,materials, and flow rates can be used depending upon the particularapplication.

This chamber also includes a wave adjustment circuit 127. The waveadjustment circuit 127 is used to provide a helical coil operating withcapacitive coupling to selected phase and anti-phase voltages. Thisportion 127 of the wave adjustment circuit coil also is shielded 140 toprevent rf from interfering with the plasma discharge or externalelements, e.g., equipment, power, etc. The coil shield 140 is made of aconductive material such as copper, aluminum, or the like. In oneembodiment, an operating frequency is selected and the wave adjustmentcircuit is dadjusted to short circuit the upper end of the helicalapplicator coil to ground 124. This provides a helical coil operating atapproximately a full-wave multiple and has substantially equal phase andanti-phase sections. This full-wave multiple operation provides forbalanced capacitance of phase 151 and anti-phase 153 voltages along thecoil 132 adjacent to the plasma source. Full-wave multiple operationreduces or even substantially eliminates the amount of capacitivelycoupled power from the plasma source to chamber bodies (e.g., pedestal,walls, wafer, etc.) at or close to ground potential.

In the present embodiment, the wave adjustment circuit 127 is a variablecoil portion 128 of a spiral transmission line, which is selectivelyplaced outside the outer shield 133. Accordingly, when the waveadjustment circuit is adjusted to become a short circuit, the plasmasource "sees" only a selected full-wave multiple comprisingsubstantially equal phase 151 and anti-phase 153 of the entireinstantaneous AC voltages 134, 135. In this embodiment, stress of thedeposited oxide film is often tensile, which can be undesirable.

Alternatively, the wave adjustment circuit 127 provides a helicalresonator operating at selected phase and anti-phase voltages that arenot full-wave multiples. This wave adjustment circuit provides for aselected amount of capacitive coupling from the plasma source to thechamber bodies. Stress of the deposited oxide film in this embodimentcan be made to be zero or slightly compressive. In some embodiments, theoxide films can be deposed with an rf plasma potential of severalhundred volts between the plasma source and the substrate to decreasethe tendency of the oxide film to absorb moisture. This can occur byadjusting the wave adjustment circuit to add in a small section oftransmission line outside of the source and correspondingly shorteningthe applicator coil (by moving the lower point at which the applicatorcoil is short-circuited and thereby decreasing the inductance of theapplicator coil and electrical length of the helical resonator 126(e.g., spiral transmission line, etc.) ). Of course, the selected amountof capacitive coupling will depend upon the application.

FIG. 4 is a simplified diagram of a resist stripper according to thepresent invention. The present stripping apparatus includes similarelements as the previous described CVD apparatus. The present strippingapparatus includes a chamber 112, a feed source 114, an exhaust 116, apedestal 118, an rf power source 122, a ground 124, a helical resonator126, and other elements. The helical resonator 126 includes a coil 132,an outer shield 133, a wave adjustment circuit 400, and other elements.The chamber can be any suitable chamber capable of housing a product 119such as a photoresist coated wafer for stripping, and for providing aplasma discharge therein. The plasma discharge is derived from a plasmasource, which is preferably a helical resonator discharge or otherinductive discharge using a wave adjustment circuit or other techniquesto selectively adjust phaseanti-phase potentials. The present strippingapparatus provides for stripping or ashing photoresist, e.g., implanthardened, etc. Further examples of such a stripping apparatus aredescribed in the experiments section below.

In this embodiment, the wave adjustment circuits rely upon open circuits(i.e., zero susceptance). Power transfer can be occurred with a balancedfeed such as an inductively-coupled push-pull arrangement such ascoupled inductors. Techniques for constructing these coupled inductorsare described in, for example, "The ARRL Antenna Book," R. D. Straw,Editor, The American Radio Delay League, Newington, Conn. (1994) and"The Radio Handbook," W. I. Orr, Editor, Engineering Ltd, Indiana(1962), which are both hereby incorporated by reference for allpurposes. In one embodiment, a ferrite or powdered iron core "balun"(balanced-unbalanced) toroidal transformer (i.e., broadband transmissiontransformer, broadband transformer, etc.) 401 can be used to providebalanced matching from a conventional unbalanced coaxial transmissionline. Techniques for constructing toroidal baluns are described in, forexample, "Transmission Line Transformers," J. Sevick, 2nd Edition,American Radio Relay League, Newington, Conn. (1990). The toroidaltransformer is coupled between the rf power source 122 and the coil 132.The midpoint 406 between the phase 405 and anti-phase voltage on thecoil is effectively rf grounded, hence it may be convenient to directlyground this midpoint of the inductive application in some embodimentsfor stability. This permits alternate operation in which power may becoupled into the inductive applicator (e.g., coil, etc.) with aconventional unbalanced feed line tapped on one side of the center.Push-pull balanced coupling ignites the plasma more easily thanconventional unbalanced coil tap matching and generally is easier toadjust in selected applications.

Referring to the helical resonator embodiments operating atsubstantially equal phase and anti-phase potentials, FIG. 5A is asimplified diagram 200 of an equivalent circuit diagram of some of them.The diagram is merely an illustration and should not limit the scope ofthe claims herein. The equivalent circuit diagram includes a pluralityof rf power supplies (V₁, V₂, V₃ . . . V_(n)) 203, representing forexample, a single rf power source. These power supplies are connected inparallel to each other. One end of the power supply is operably coupledto a ground connection 201. The other end of the power supplies can berepresented as being connected to a respective capacitor (C₁, C₂, C₃ . .. C_(n)). Each of these capacitors are connected in parallel to eachother. During this mode of operation, substantially no voltagedifference exists between any of these capacitors, as they are allconnected to each other in parallel.

FIG. 5B is a simplified diagram of instantaneous AC voltage and currentalong a helical resonator coil of FIG. 5A where each end of theinductive applicator is short circuited. The diagram is merely anillustration and should not limit the scope of the claims herein. Thisdiagram includes the discharge tube 213 and an inductive plasmadischarge (or plasma source) 501 therein. As shown, the plasma dischargeincludes an intensified "donut-shaped" glow region 501 that occupies alimited range (R) of the discharge tube 213. The plasma discharge has anaverage voltage potential (V_(ave)) of substantially zero volt betweenthe ground potential (V_(G)) and the high voltage potential (V_(H)). Ascan be seen, the plasma discharge 501 has capacitively coupling elementsto V_(H) and V_(G). But the average voltage potential of this plasmadischarge is zero. This operation provides for balanced capacitance ofphase 503 and anti-phase 505 voltages along the coil adjacent to theplasma, thereby substantially preventing capacitively coupling from theplasma source to chamber bodies. As also shown, a current maxima 507exists at V_(ave), which corresponds to an inflection point between thephase 503 and the anti-phase 505.

In an alternative operating mode, dim rings of plasma caused byinductively coupled plasma current are visible near top and bottomextremes of the inductive application, as illustrated by FIG. 5C. Thisoperating mode is generally for a full-wave 517 inductive coupling coiloperated at a very high power, e.g., maximum power input to theinductive applicator is often limited by thermal considerations andbreakdown. The rings 513, 515 of current in the plasma discharge aresimulated by maximum coil current areas corresponding to voltage minimaat the top and bottom shorted ends of the coil. Under these high powerconditions, subordinate current rings are detectable and some excitationis often visible in the intermediate regions. This excitation ispartially caused by capacitively driven currents within the dischargecoupled to the voltage maximum and voltage minimum positions along theinductive applicator.

Alternatively, subordinate inductive plasma current rings at the top andbottom ends 513 of the resonator do not appear with limited input power.The coil current and inductive flux fall beyond the ends of theinductive applicator so that a single inductive ring 515 in the centerportion is more stable, provided that the conductivity of the plasma islarge enough to support a single current ring at a specified inputpower.

In alternative applications using high power operation, no secondaryplasma current rings may be desirable. These applications often havesubstantially minimum internal capacitive coupling. In theseapplications, the inductive applicator (e.g., coil) abutting the vacuumvessel may be shortened from a full wave to an appropriate length suchthat only the central current maxima exists on the coil abutting theplasma source and the potential difference between maximum and minimumvoltage on the applicator is substantially reduced. The presentapplication is achieved by stabilizing the desired waveform along theapplicator by appropriate impedance wave adjustment circuits.

Referring to the above embodiments, the present invention provides forprocessing with an inductively coupled plasma in which the plasmapotential from coupling to a phase portion of the inductive applicatoris substantially not offset by capacitive coupling to anti-phasevoltages on selective portions to the inductive coupling element.Conventional inductive sources (e.g., conventional helical resonators,etc.), however, have hitherto been operated in quarter-wave or half-wavemodes. These modes provide only phase capacitive coupling to the plasma,which raises the plasma potential toward the coil without compensationanti-phase coupling. Conventional inductive sources that are longer thana half-wave have been generally considered cumbersome and impracticalfor plasma reactors. In particular, these inductive sources are large insize, and have nodes along the helical coil, which have been believed tocreate a non-uniform plasma. In order to operate a substantiallyinductive plasma in a helical resonator, conventional inductive sourcesrelied upon shielding the plasma tube from electrical fields originatingon the coil. Shielding occurred, for example, by inserting alongitudinally split shield between the coil and plasma tube.

The present invention provides for a substantially pure inductivelycoupled power source. A benefit of this inductively coupled power as aprimary means to sustain plasma excitation is that electric field linesproduced by inductive coupling are solenoidal (e.g. they close onthemselves). Since solenoidal electric field lines have zero divergence,they do not create or support a scalar potential field (e.g. a voltagedifference) within the plasma volume. Thus, in an ideal case,inductively coupled power can be transferred into a plasma without nodirect relationship between the plasma potential and the voltages oncoupling elements (e.g. the voltage on the coil in a helical resonator)or voltages on rf matching networks, if such are used. Furthermore, whentransferring power to the plasma by purely inductive means, powertransfer does not require any significant potential difference to bemaintained between elements of the plasma and ground potential (e.g. thepotential difference between the plasma and ground can be fixed byfactors which are substantially independent of inductive excitationpower). Although in theory, inductive power transfer does not requireraising the AC or DC potential of the plasma with respect to ground, inpractice there has been substantial shift and harmful alteration in theplasma potential found in unshielded current art inductive sources.

As previously noted, and further emphasized herein, the most effectiveconventional method employed to avoid plasma potential shift inconventional commercially available inductive sources is to shield theplasma from the electrical fields on the inductive coupling element(commonly a multi-turn coil) by inserting a grounded conductive memberbetween the inductive driving element and the plasma discharge tube.Shielding is, however, cumbersome and inconvenient and has seriousdisadvantages in practice. Shields couple to inductive applicatorelements and can cause wide excursions in the natural resonancefrequency, which are not predicted by conventional design formulae. Thisoften results in laborious trail and error and iterative mechanicaldesigns to achieve a desired resonance. Another disadvantage ofshielding is that shields often make it difficult to achieve initialignition of the plasma since shields generally exclude capacitiveelectric fields in the plasma discharge tube. In particular, ignition(known as plasma breakdown) of inductive breakdown generally begins witha capacitive electric field discharge, which is stable at lower currentsand powers (S, for example, J. Amorim, H. S. Maciel and J. P. Sudana, J.Vac. Sci. Technol. B9, pp. 362-365, 1991). Accordingly, shields tend toblock capacitive electric fields, which induce plasma ignition.

Insertion of the shield close to high voltage RF point in a network(such as the voltage maximum points in a helical resonator or the highpotential driven side of a TCP coil) also causes large displacementcurrents to flow through the capacitance between the shield and coil.This high potential difference is also a potential cause of damaging rfbreakdown across the air gap, hence the gap may require protection byinconvenient solid or liquid dielectric insulation. The displacementcurrent flow causes power loss and requires that higher power RFgenerating equipment be used to compensate for the power loss. Couplingloss in the plasma source structure is also undesirable from thestandpoint of thermal control. These limitations are overcome by thepresent invention using the wave adjustment circuits, an inductiveapplicator of selected phase length, and other elements.

Experiments

To prove the principle and demonstrate the operation of the presentinvention, a helical resonator plasma source was used in a photoresiststripper. Conventional helical resonators also were evaluated in theseexperiments. These experiments are merely examples, and should not limitthe scope of the claims herein. One of ordinary skill in the art wouldeasily recognize other experiments, uses, variations, and modificationsof the inventions defined by these claims.

I. Conventional Photoresist Stripper

In this experiment, the conventional resist stripper was a prototypemade by MC Electronics, present assignee. Of course, other stripperplatforms also can be used depending upon the application. Aconventional quarter-wave helical resonator resist stripper 600 wasconstructed with a quarter-wave helical resonator source 602 upstream ofa processing chamber 604, shown in FIG. 6. This quarter-wave helicalresonator 602 included a coil 608 and other elements.

Coil 608 consisted of 5.15 turns of 0.4 inch diameter copper tubingwould with a pitch of 0.5 turns per inch with a mean radius of 6.4inches and centered radially and vertically inside an outer coppershield 610. Coil 608 is operably coupled to a power source 612 andoperated at about 13 MHz radio frequency. A 17 inch long, 9.25 inchdiameter quartz tube 606 was centered inside of the copper coil 608. Theshield 610 was 16 inches inside diameter, approximately 0.08 inchesthick and 18 inches long. This shield 610 also was connected to a ground(V_(G)) connection on the aluminum process chamber body (except whenmaking the current measurements described below).

The process chamber 604 was for a conventional resist stripper. Thisresist stripper included a wafer support 616 (or pedestal) and otherelements. Process chamber 604 is operably coupled at an outer location620 to ground via shield 610. Wafer support 616 has a wafer 618 disposedthereon.

The wafer 618 is a 6-inch (250 mm) <100> type wafer with approximately1.25 microns of spin-coated Mitsubishi Kasei positive photoresistMPR-4000. This wafer was ashed on the grounded 10 inch diameter wafersupport 616. This support was resistivity heated and the temperature ofthe substrate support was sensed with a thermocouple.

After the helical resonator plasma was ignited, visible plasma filledthe quartz plasma tube under all of the conditions used for processing.In addition, a strong plasma glow was always visible above the wafer inthe downstream processing chamber which was indicative of secondaryplasma discharge to the substrate support. This secondary plasmadischarge was also accompanied by current flow from the resonator shieldto the chamber of approximately 5-10 Amperes rms (and sometimes evenmore) which could be measured by elevating the shield on insulatingblocks and monitoring the current flow through a 2 inch long 1.5 inchwide strip of copper braid which was passed through a Pearson Currentprobe used to monitor the current.

FIG. 7 is a simplified diagram 700 of the rf voltage distribution alongthe coil for the quarter-wave helical resonator of FIG. 6. This diagramincludes the quartz tube 606 and a plasma discharge (or source) 701therein. As shown, the plasma discharge includes a glow region that 701occupies a large range (R) of the quartz tube 606. The plasma dischargehas an average voltage potential (V_(ave)) between the ground potential(V_(G)) and the high voltage potential (V_(H)). As can be seen, theplasma discharge 701 has capacitively coupling elements to V_(H) andV_(G) due to its average voltage potential V_(ave). In fact, aspreviously noted, the current flow from the resonator shield to thechamber was at least 5-10 Amperes rms. In high power applications,intense sparking was observed in the chamber from the capacitivelycoupled plasma source.

II. Present Photoresist Stripper

To prove the principle and operation of the present inventions,experiments were performed. These experiments used a photoresiststripper apparatus. This resist stripper apparatus in a cluster toolarrangement used a helical resonator according to the presentinventions. One of ordinary skill in the art, however, would recognizethat other implementations, modifications, and variations may be used.Accordingly, the experiments performed herein are not intended to limitthe scope of the claims below.

The photoresist stripper apparatus was configured with multiple processchambers in a cluster tool arrangement, as illustrated by FIGS. 8 and 9.FIGS. 8 and 9 illustrate a simplified top-view diagram 800 and asimplified side-view diagram, respectively. Two process chambers, e.g.,chamber 1 901 and chamber 2 903, were used. Chamber 1 901 was used forstripping implant hardened resist crust (or skin). Chamber 2 903 wasused for stripping the remaining photoresist. Alternatively, thechambers can be both used for stripping implant hardened resist crustand stripping remaining photoresist. Of course, the particular usedepends upon the application. These chambers also were made of aluminumwith ceramic inserts, which is highly resistant to chemical attack.

The apparatus also used a microprocessor based controller to overseeprocess operations. This microprocessor based controller can be accessedthrough a control panel 921. The present apparatus used a controllermade from a 486DX processor PC made by EPSON, with a color LCD touchpanel display. This controller also is shielded and highly resistant tochemical attack.

An automatic wafer handling system 910 was also provided. The automaticwafer handling system used standard cassettes 912 for transferring thephotoresist coated wafers to and from the process chambers 901, 903. Theautomatic wafer handling system included a robot 917, cassette chamber 1905, cassette chamber 2 907, cassette stage 1 909, cassette stage 2 911,and other elements. The wafer handling system 910 used a conventionalinterlock system for providing the cassettes 912 from the cleanroom intothe process chambers 901, 903. A main shuttle chamber 913 housed therobot 917 in the cluster tool arrangement. The controller oversees theautomatic wafer handling system operations. The present wafer handingsystem is made by JEL Co., LTD of Japan.

A cooling plate 915 was included in the main chamber 913 housing therobot 917. The cooling plate 915 was of conventional design, and wascapable of cooling the wafer after being stripped, which often occurs atelevated temperatures. Alternatively, the cooling plate can be used tothermally adjust the wafer temperature either before, after, or evenbetween selected process operations.

The process chambers 901, 903 were disposed downstream from respectiveplasma sources 923, 925. Each helical resonator included a coil 927disposed around a quartz tube 929. The coil consisted of 11.5 turns of0.4 inch copper tubing wound with a pitch of 0.9 turns per inch with amean radius of 9.4 inches and centered radially and vertically inside anouter copper shield 931. The coil is operably coupled to a power source(not shown). A 17 inch long, 9.25 inch diameter quartz tube was centeredinside of the copper coil. The shield was 16 inches inside diameter,approximately 0.08 inches thick and 18 inches long. The shield isoperably coupled to a lower portion of the coil.

In one experiment, processes were used for stripping photoresist fromwafers, e.g., See FIG. 9 reference numeral 933. The processes involvedthe use of a multi-step stripping operation to remove implantedphotoresist from semiconductor wafers. Samples were prepared usingeight-inch wafers. These wafers were spin coated with Mitsubishi Kaseipositive photoresist MPR-4000. Spin coating occurred at 1,200 rpm and120° C. for 90 seconds. The resulting photoresist was about 1.2 micronsin thickness in the sample wafers. These sample wafers were implanted toform a implanted hardened resist layer near the top of the photoresist.

An implant resist stripping process was performed to remove the topimplant hardened resist. This occurred by stripping using an"un-balanced" phase and anti-phase coupling relationship in a half-wavehelical resonator. The half-wave helical resonator was configured in oneof the process chambers. In this chamber, the pedestal had a temperatureof about 40° C. to maintain a low wafer temperature. This low wafertemperature was maintained to reduce the possibility of "popping."Popping occurs when vapor in the underlying photoresist explodes throughthe implant hardened resist.

After the top hardened layer was removed. The wafer was transferred intoa chamber operating at a full-wave multiple. This chamber operated at afrequency of about 27.12 MHz at a full-wave multiple. The pedestal ofthis chamber was at 150 to 200° C. The full wave structure provided forbalanced phase and anti-phase coupled currents, thereby reducing theamount of capacitively coupled plasma, which can be detrimental to theunderlying substrate. In this step, overashing was performed tosubstantially remove all photoresist material from the wafer. No damageoccurred to the underlying substrate during this overashing step.

Once the photoresist has been stripped, the wafer is cooled. Inparticular, the wafer is removed from the full-wave multiple processchamber, and placed on the cooling station. This cooling station reducesthe temperature of the wafer (which was heated). This wafer is thenreloaded back into its wafer cassette. Once all wafers have beenprocessed in the cassette, the cassette comprising the stripped wafersis removed from the cluster tool apparatus. Characteristics of thishalf-wave helical resonator were described in detail above. In thepresent experiments, the following tests also were performed.

Test 1: 6-inch wafers were ashed at a total pressure of 0.13 Torr usinga gas flow of 0.2 standard liter per minute of pure oxygen, forward rfpower of 2200 watts and a reflected power of 150 watts at an excitationfrequency of 13.4 Mhz. The substrate was held at 60° C. and wafers wereashed and then the discharge was extinguished). The ashing rate acrossthe wafer was determined to vary between approximately 3411 Å/min and3139 Å/min with the rates approximately symmetric about the center ofeach wafer and the maximum ashing rate at the center. The averageetching rate was 3228 Å/min and etching uniformity was approximately 4percent.

Test 2: 6-inch wafers were ashed at a total pressure of 1 Torr using agas flow of 1 standard liter per minute, forward rf power of 2200 wattsand a reflected power of 160 watts at an excitation frequency of 13.0MHz. The substrate was held at 60° C. and the ashing rate was determinedto very between approximately 3144 Å/min and 3748 Å/min depending onposition on a wafer. The etching uniformity was approximately 9 percent.

Test 3: Resist coated wafers were implanted with a selected dose of5×10¹⁵ atoms/cm² at 40 kev arsenic (As). The wafers were cleaved intosamples approximately 3 centimeters square. Two samples were then ashedon the substrate support simultaneously, under the various conditionslisted in Table 1.

                  TABLE 1                                                         ______________________________________                                        Experimental Results for Ashing                                                                    O.sub.2                                                                             Fwd   Refl. rf                                          Time(s) Pressure                                                                              Flow  Pwr   Pwr   freq. Temp                             Run  (sec.)  (Torr.) (slm)*                                                                              (W)   (W)   (MHz) (C.)                             ______________________________________                                        A    180     0.23    0.5   2,000 180   13.2  68                               B    132     0.06    0.2   2,150 180   13.3  90                               C    180     0.13    0.2   2,200 150   13.3  60                               D    300     0.13    0.2   2,200 150   13.3  40                               E(I) 90      0.09    0.1   2,200 80    13.4  40                               F(II)                                                                              150     0.09    0.1   2,200 80    13.4  40                               ______________________________________                                         *slm = standard liters per minute (or 1000 sccm)                              (I) Unimplanted resist was used in this test and ashing was terminated        before endpoint was reached to test unifomrity. The average ashing rate       was 5259 Å/min and uniformity was 7.5%.                                   (II) Implanted resist was etched for 150 sec, but endpoint was visible at     100 seconds.                                                             

Under conditions used for Run D, it was determined that resist wascleared from the entire wafer after 3 minute and 15 seconds.Consequently, the ashing time in the table included approximately 100sec. overetching. Under conditions where practical ashing rates wereattained, a visible plasma discharge and sheath could be observed overthe wafer.

Diagnostic measurements of current similar to those performed in theconventional stripping apparatus were performed. In these measurements,currents from the shield of the resonator to the processing chamber gavevalues of at about 0.1 to 0.5 Amperes rms and less. These measurementswere limited by error using available instrumentation. Accordingly,these currents were at least an order of magnitude below those currentsmeasured above in the conventional stripping apparatus.

A visual inspection of the stripped wafers shows extremely good results.That is, the wafers were stripped at a sufficient rate for productionoperation and no substantial damaged occurred to the wafers. Thisprovides for effective wafer tum-around-time and substantially no damagecaused by the plasma. In addition, current measured from the shield tothe chamber by elevating the shield on insulating blocks was less thanabout 0.5 Amperes rms and, in some instances, at or below measured errorusing available instrumentation. This current was substantially lessthan those measured in the conventional stripping apparatus.

While the invention has been described with reference to specificembodiments, various alternatives, modifications, and equivalents may beused. In fact, the invention also can be applied to almost any type ofplasma discharge apparatus. This discharge apparatus can include anapparatus for plasma immersion ion implantation or growing diamonds,TCPs, and others. This discharge apparatus can be used for themanufacture of flat panel displays, disks, integrated circuits,diamonds, semiconductor materials, bearings, raw materials, and thelike. Therefore, the above description should not be taken as limitingthe scope of the invention which is defined by the appended claims.

What is claimed is:
 1. A process for fabricating a product using aplasma source, said process comprising the steps of subjecting asubstrate to entities, at least one of said entities emanating from agaseous discharge excited by a high frequency field from an inductivecoupling structure in which a phase portion and an anti-phase portion ofcapacitive currents coupled from the inductive coupling structure areselectively balanced;wherein said inductive coupling structure isadjusted using a wave adjustment circuit, said wave adjustment circuitadjusting the phase portion and the anti-phase portion of thecapacitively coupled currents.
 2. The process of claim 1 wherein thewave adjustment circuit selectively adjusts a frequency of an rf powersupply.
 3. The process of claim 1 wherein the high frequency field isadjusted using a variable frequency power supply.
 4. The process ofclaim 1 wherein the wave adjustment circuit comprises a transmissionline.
 5. The process of claim 1 wherein said process is provided in achamber.
 6. The process of claim 5 wherein the chamber is provided for aprocess selected from etching, deposition, sputtering, or implantation.7. The process of claim 1 wherein said inductive coupling structureprovides a wave multiple selected from a one-sixteenth wave, aone-eighth-wave, a quarter-wave, a half-wave, a three-quarter wave, anda full-wave.